Mold Sampling

• Bulk sample-piece of material with suspected mold growth
• Surface sample: a sample taken from a surface to determine if mold is present
• Viable-able to grow
• Air sample- a sample air taken to determine the level of bio-aerosols
• Water sample-sample of water taken to determine levels of bacteria mainly

Why Sample?

Sampling is a crucial part of mold remediation work because most, if not all, bioaerosols are invisible to the naked eye. This can make it very difficult to determine the extent or existence of a mold contamination problem by relying only on the physical senses. To overcome this inability, samples are taken of the air, water, and surfaces in an area suspected of having mold contamination. These samples are then analyzed in various ways to determine if the mold problem exists.

Types of Samples

• Viable – Cultured for 7-12 days
• Nonviable-24 hour to 3-day results
• Bulk , tape, wipe , swab, scrape samples
• Air Samples- Cultured, standard impact, cassette impaction
• Outdoor vs. indoor air

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Viable vs. Non-Viable

Viable spores are those that are capable of growing into a colony, given the correct conditions. These are the only spores that show up on culture samples, where they are called colony-forming units (cfu). They are usually a minority of the total number of airborne spores.

Non-viable spores are spores that are not capable of growing. Many species of mold produce large numbers of non-viable spores because certain conditions (i.e., substrate nutrients, pH, relative humidity, presence of other molds or chemicals, etc) affected the growth process. Non-viable spores may not be visually distinguishable from viable samples, and they cause the same allergic effects as viable spores. Non-viable spores will not be counted in culture samples. To get a count of non-viable spores a spore trap of some type must be used so that a microscopic analysis can be completed.

Viable v. Non-viable Sampling

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Bulk and Surface Samples

Bulk samples are pieces of material that have mold growth on them, or are suspected of having mold growth visual inspection is enough to identify apparent fungal growth, however, a sample will have to be collected for analysis to determine the mold type. Once in the lab the bulk sample can be prepared for analysis in a number of different ways. For viable sample analysis a small area is precisely measured and the surface cut or scraped into a nutrient solution and “plated” onto a petri dish. After incubation and analysis the results will be reported as cfu/cm 2.

Bulk samples can also be prepared for analysis by non-viable methods. This can be done with a tape sample or a microvacuum sample. Tape and microvacuum samples are considered to be surface samples although they are often used as a laboratory preparation technique for bulk samples.

Surface samples are samples taken directly from a surface suspected of having mold or microbial growth. Surface samples are primarily useful for determining what fungal agents are present on the surface. They do not give reliable indications of airborne spore concentration. However, surface samples can share if there has been an extensive deposition of fungal material through the air.

Tape samples can be collected to identify mold growth on a surface. A piece of tape is stuck to the surface, then removed. Any particles or spores on these surfaces should be stuck to the tape. The tape is then put onto a slide and analyzed under a microscope.

Microvacuum samples are taken from a surface using a slit sampling cassette contains a slide with a sticky substrate, where any particulates or bioaerosols are captured. The cassette is placed just above the surface and the pump is turned on for a short time. Once there is a visible trace on the cassette, it is put onto a slide and analyzed under a microscope.

Swab samples are a method of surface sampling used to identify both mold and bacterial growth. To take a swab sample, the surface to be tested is rubbed with a swab that is then rubbed onto an agar plate. The mold and/or bacteria grow on the plate and are visually identified.

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Air Samples

Air samples are taken to determine airborne spore levels. There are many ways to take air samples, including inertial impaction, multiple hole or sieve impactors, slit samplers, centrifugal sampler, liquid impingement, filtration, and gravitation or settling.

Air samples show only what is in the air at the time the sample is collected. Some types of fungi, such as Stachybotrys, have “sticky” spores that do not become airborne easily. These fungi may not show up in air samples even if they are currently growing in the area.

Air samples fall into two general categories. The first type uses a culture medium of some sort to collect the airborne spores. The spores are allowed to grow and the resulting colonies are counted and identified. Each growth area seen on the plate is known as a colony forming unit (cfu). Since the amount of air drawn through the sampler is carefully documented and the areas of fungi growth on these ample precisely counted, a conversion factor can be used to calculate the number of cfus per cubic meter of air (cfu.m3).

Culture samples have advantages and disadvantages. An advantage is that counting and identifying the colonies that grow can be done in such away as to identify both the genus and the species of the organism. On the other hand, these samples do not include non-viable spores, even though such spores can still cause health problems. Culture samples take several days for the mold to grow, so there can be no rush turnaround time.

The other general category of samplers is those that affix spores to a sticky medium, which is then analyzed under a microscope. Any spores observed are identified and counted, and then a conversion factor is used to calculate the number of spores per cubic meter of air.

This method includes both viable and non-viable spores, so it can be a more accurate indication of airborne spore levels. The analysis can be performed immediately after the sample is taken, so rush turnaround time is possible. However, direct microscopy is usually limited to designation of mold at the genus level and generally cannot be used for bacteria.

Water samples are taken to determine the presence of bacteria, such Legionella and E.coli. The samples also detect bacterial toxins, such as endotoxins.

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Sampling Plans

A sampling plan is a description of where, when and how an investigator proposes to test his or her hypothesis.

A good sampling plan includes specifications of the biological contaminants under study, typical sources and reservoirs of the suspected agents, and the expected concentration and variability of the materials being sampled. The plan should also include the analytical methods that will be used to detect, identify, and quantify each suspect material, as well as the sampling methods to be used. The operating parameters of all sampling instruments and the locations and times at which samples will be collected should also be included in the plan.

A good sampling plan should take into account the strengths and weaknesses of each sampling method, and use them to complement each other as much as possible. It may not be possible to meet this ideal on every project due to constraints on time, manpower instruments, analytical resources, budget, and building access. With the variability in sampling methods and analytical techniques it is often best to have sampling plans designed by experienced professionals. Regardless of who develops the plan, a goal or theory should be identified before the plan is finalize so that the result scan be interpreted to answer questions rather than serve a mere data points.

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Laboratory Analysis

The analysis of samples in the laboratory provides a major portion of the data that is produced during a mold investigation and is used to guide the remediation contactors. This involves analyzing samples under the microscope, and counting and identifying any colonies that grow on an agar plate.

Once the samples have been analyzed the investigator needs to do several things. First, he must check and validate the data, striking observations. Second, the investigator should summarize or reduce the data into tables or a few short paragraphs. Finally, the investigator should estimate the data’s reliability and look for any statistically significant association and differences.

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Data Interpretation

After all samples have been collected and analyzed, the investigation enters the data interpretation phase. During data interpretation, the investigator must make several decisions. He must decide on the relevance of the observations to human exposure. Are any of the observations a cause of concern? The investigator must decide how strong the association is between any health concerns and exposure to any molds detected in the air. The probability of any current or future risks should be calculated. The final step in the data interpretation phase is making recommendations of measures that can be taken to prevent further exposure and eliminate problems. The investigators should not rely completely on statistical evidence to determine if a mold problem is present. A problem may exist even if there statistical evidence does not show it. On the other hand, statistical significance does not, in itself, mean that results have any real-world importance. The investor must be able to apply knowledge, expert advice, training and experience when analyzing data to recognize if a problem really exists and is supported by the sampling evidence.

Ideally, once it as been decided that mold is the likely source of the symptoms observed in the problem area, the investigator should be able to document three main things.

The first is the contaminant itself. The investigator should be able to point to a specific mold as the probable cause of the problem. Of course, but the investigator should be able to define the most logical or reasonable cause of the observed problems.

The second main area of documentation is the local source of the mold. The investigator should be able to determine where the agent is coming from originally, and any other areas where it exists in the problem area. This makes correcting the problem much simpler.

The third and final area of documentation is exposure. The investigator should be able to show that people in the problem are aware exposed to sufficient amounts of the agent to cause the observed symptoms. Without this step, the first two steps are of little or no use.

All the above information points to a plan for remediation of the problem. If the agent can be positively identified and its source pinpointed, clean up and removal is relatively straightforward. Well thought out sampling plan executed properly by a trained specialist will result in a good data. This data, when properly interpreted in light of experience and training, will lead to effective recommendations for remediation.

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Post Remediation

In order to successfully complete remediation project, it is important to have clear goals in place from the very beginning. These goals should specify things like acceptable airborne spore counts and types, so that remediation efforts can be focused.(Note: reasonable post-remediation sampling criteria allow for some level of airborne/surface contamination due to the ubiquitous nature of mold an other biological materials) Once the goals are met, the project is successfully finished. It may be prudent to re-test the air periodically for a while after the project, to ensure that the problem molds have truly been removed.